Flexible installation of a hydrocarbon liquefaction unit

ABSTRACT

Natural gas liquefaction unit including at least one cryogenic cold box having at least one heat exchanger; a fixed assembly zone on its outer wall; at least one closed loop nitrogen refrigeration cycle; at least one device for equipment required for implementing the liquefaction of a natural gas stream from a hydrocarbon supply stream; at least one interconnection module comprising a pipe holder means and a set of pipes and valves, designed to connect said at least one cold box to at least one equipment device for the cycle for refrigerating and/or separating C6+ type hydrocarbon elements contained in the natural gas, wherein the interconnection module rests on a frame allowing it to be handled and is connected to the cold box and to the other method or equipment sub-assemblies located around said fixed assembly zone.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to French Patent Application No. 2003456, filed Apr. 7, 2020, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The technical field of the invention is that of the liquefaction of natural gas using a nitrogen refrigeration cycle.

The present invention relates to an installation of a natural gas liquefaction unit using a nitrogen refrigeration cycle and its unit.

BACKGROUND OF THE INVENTION

Natural gas liquefaction methods need to be used in order to reduce the environmental impact. Market developments promote the use of liquefiers close to public areas in order to ensure more efficient management of deliveries. The available land is generally small and must meet strict environmental restrictions.

Commonly, this type of unit uses mixed coolants that are mixtures of gas with high yields for the liquefaction of natural gas. However, their hazardousness results in factory configurations that are very spread out with a very high societal risk. The invention defines the design of Natural Gas liquefiers using a nitrogen refrigeration cycle called Turbofin™.

SUMMARY OF THE INVENTION

The invention offers a solution to the aforementioned problems. An aspect of the invention relates to a natural gas liquefaction unit comprising:

-   -   at least one cryogenic cold box comprising:         -   at least one heat exchanger;         -   a fixed assembly zone on its outer wall;     -   at least one closed loop nitrogen refrigeration cycle;     -   at least one device for equipment required for implementing the         liquefaction of a natural gas stream from a hydrocarbon supply         stream;     -   at least one interconnection module comprising a pipe holder         means and a set of pipes and valves, designed to connect said at         least one cold box to at least one equipment device for the         cycle for refrigerating and/or separating C6+ type hydrocarbon         elements contained in the natural gas;         characterized in that the interconnection module rests on a         frame allowing it to be handled and is connected to the cold box         and to the other method or equipment sub-assemblies located         around said fixed assembly zone.

According to other embodiments, the present invention also relates to:

-   -   a unit as defined above, characterized in that the         interconnection module particularly comprises one or more         elements selected from among control valves, manual valves,         sample connections, pipes, pre-cut panels with valve actuators,         instruments, vapour sources, lighting, ladders and platforms,         pre-wired junction boxes, platforms for instrument/electric         cables, pipe supports, channeling;     -   a unit as defined above, characterized in that the         interconnection module comprises one or more elements selected         from among control valves; manual valves, valve actuators;     -   a unit as defined above, characterized in that said other method         or equipment sub-assemblies are required to implement at least         one method function selected from among the compression of the         nitrogen of the refrigeration cycle, the overpressurization of         the nitrogen of the refrigeration cycle, the expansion of the         nitrogen of the refrigeration cycle, the cooling of the nitrogen         of the refrigeration cycle, the liquefaction of the natural gas         stream, the separation of the C6+ type hydrocarbons contained in         the natural gas, the interconnection module being devoid of such         method or equipment sub-assemblies. In other words, the         interconnection module does not comprise any method or equipment         sub-assembly as defined above. In particular, the         interconnection module is devoid of a separator module;     -   a unit as defined above, characterized in that the refrigeration         cycle comprises a first means for compressing the nitrogen of         the refrigeration cycle, a means for cooling the nitrogen of the         refrigeration cycle, a second means for compressing the nitrogen         of the refrigeration cycle, said second compression means         comprising two booster compressors coupled to two respective         expansion means, said booster compressors being configured to         compress the nitrogen of the refrigeration cycle at an identical         pressure;     -   a unit as defined above, characterized in that said frame has a         metal structure;     -   a unit as defined above, characterized in that said at least one         heat exchanger is a brazed aluminium heat exchanger;     -   the use of a unit as defined above for liquefying a natural gas         stream.

A method for starting a liquefaction unit as defined above, comprising the following steps:

-   -   on-site installation of a closed loop nitrogen refrigeration         cycle and of a cold box comprising:         -   at least one heat exchanger;         -   a fixed assembly zone on its outer wall;     -   on-site installation of an interconnection module comprising a         pipe holder means and a set of pipes and valves, designed to         connect said at least one cold box to at least one equipment         device for the cycle for refrigerating and/or separating C6+         type hydrocarbon elements contained in the natural gas,     -   fixing said interconnection module to the cold box and to at         least one equipment device, allowing the implementation of the         liquefaction method using said cold box, already available on         the site.

The natural gas is composed of different gases with different physical features, Nitrogen is a pure substance and does not allow all the compounds of the natural gas to be tracked for the liquefaction thereof. However, the method allows the use of the “compression-expansion” principle and therefore allows cold production with high liquefaction yields.

The method is composed of two main parts. The cold creation part identified by the name ‘nitrogen cycle’ and the natural gas liquefaction part. A nitrogen refrigeration cycle is understood to be a cycle in which the coolant is nitrogen, contrary to the cycles with mixed coolants, in which the coolant is a mixture of different constituent elements, in particular a mixture of hydrocarbons.

The nitrogen cycle is a closed loop. The natural gas only passes through the liquefaction zone, called cold box. The nitrogen of the cycle is compressed in a compressor, then cooled, before being compressed a second time, by two boosters, or booster compressors, coupled to two separate turbines.

Preferably, the output pressure of the two boosters of the turbines is identical. Contrary to the configurations in which the outputs of the cold and hot turbines have different pressures and are therefore compressed at two different stages of the cycle compressor, this allows only a single suction pressure to be processed, which simplifies the architecture of the unit and improves its operational efficiency, by simplifying the operating and maintenance operations.

The nitrogen is then pre-cooled before being expanded to create two different cold temperatures. These two latter temperatures correspond to two liquefaction temperatures. Said temperatures themselves correspond to two average temperatures for liquefaction of the gases composed of the natural gas.

Each compression stage corresponds to the heating of the gas. In order to optimize the next compression, the gas must be pre-cooled using equipment called “refrigerators”, operating by exchanging with air or with water.

The consequence of this type of liquefaction is the significant number of connections connecting the equipment to each other. This configuration results in a significant cost compared to the size of the liquefaction cycle.

The liquefaction comprises one or more exchangers, as well as, in general, an element allowing separation of the heavy C6+ type hydrocarbon components contained in the natural gas. The gas that is thus purified, basically composed of methane, is recovered in order to be liquefied through exchangers located in said cold box. The aforementioned separation equipment is located in the same insulating assembly, called cold box.

The liquefaction assembly called cold box can, as a function of the liquefaction volumes, be composed of one or more cold boxes. These can be vertical or horizontal.

The aforementioned equipment and/or sub-assemblies are located around a distribution module comprising all the connections between all the equipment that are required for the method, as well as the connections to the outside of the liquefaction assembly. AH the elements allowing the measurements and the liquefaction assembly to be controlled are also located in this sub-assembly, called central module.

The machines called turbine/booster machines may or may not be, as a function of their capacities, located on the same support structure.

Each of these satellite modules comprises the method function for which it has been identified, as well as the elements allowing it to be controlled and enabling its intrinsic safety.

The connection between the central module and the satellites is adapted for each project condition and/or for each physical variation of each of these satellite modules.

The present invention allows the interconnection zone to be defined as a central distribution module between all the method modules. This can cover the equipment associated with the method or other modules comprising method sub-assemblies. These other method or equipment sub-assemblies are those that are configured to implement method functions that are required for implementing the cold fluid required for the liquefaction of a natural gas stream. The method functions are clearly separate from each other, as well as from those that are associated with the designs of each supplier, and the interconnection allows the possibility of changing suppliers without necessarily changing the circulation of the fluids. The connections are adapted to the modules during the on-site assembly.

In order to meet this requirement, the sub-assemblies and satellite equipment are designed to be autonomous and independent from a method perspective, but also to be mechanical.

The present invention allows a natural gas liquefaction installation to be provided using a nitrogen cooling cycle that adapts to the environment in a manner that is simple and is the least expensive, By virtue of the invention, the system allows a flexible arrangement to be proposed for the installation as a function of the environment.

This also makes it possible to ensure the effectiveness of the method irrespective of the type of hydrocarbon, in particular natural gas.

This also makes it possible to guarantee construction with a manageable cost, since the modules can be constructed in the factory and delivered directly to the site, while being able to be adapted to the environment of the site.

A cold box integrates one or more heat exchangers in an insulating enclosure that is generally made of steel or of carbon. The cold box combines the exchangers with their associated cryogenic equipment: separator tanks, two-phase supply tanks, distillation columns, connection pipes, valves and instrumentation.

Therefore, the present invention allows the aforementioned problem to be resolved in at least two points:

-   -   The number of pipes forming the connection between equipment         leads to an assembly cost and a significant impact on the         overall cost of the installation.     -   a. The present invention allows the interconnection zone to be         defined as a central distribution module between all the modules         required for the method.     -   b. This separation between the “method functions” (Compression,         Overpressure, Expansion, Cooling, Liquefaction), which are         associated with the designs of each supplier, and the         interconnection enables the possibility of changing suppliers         without necessarily changing the circulation of the fluids. The         connections are adapted to the modules during on-site assembly.     -   In order to monitor the evolution that is desired by the user         without having to modify the general design of the path of the         fluids, each module must be able to have an acceptance threshold         for the external stresses.

The present invention will basically cover the cryogenic part of the method. It forms the liquefaction area thereof. In order to limit thermal losses, this part of the method is installed in an insulating box, called cold box. The temperatures vary between +20° C. to −196° C. The equipment is therefore subject to significant mechanical stresses. In order to reduce the mechanical effects, it is common to distribute the stresses over the whole of the relevant method line. The solution implemented in the present invention allows an approach for managing stresses to be provided by defining the cold box as being autonomous. The stresses inside the cold box will be managed by placing a fixed point at the limit of the cold box or by providing permissible stresses for other parts.

This installation allows the cold-part modules (heat-exchange module and separator module) to be aligned together and allows the hot part (compressor module) to be added in line with or perpendicular to this alignment, thus reducing the ground footprint and also reducing the lengths of the interconnections.

The invention and the various applications thereof will be better understood from reading the following description and from studying the accompanying FIGURES.

BRIEF DESCRIPTION OF THE FIGURES

For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

The FIGURE shows a representation of a schematic diagram of a liquefaction system according to one embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a representation of a schematic diagram of a liquefaction unit according to one embodiment of the invention.

In FIG. 1, the hydrocarbon fluid liquefaction unit 1 comprises:

-   -   at least one cryogenic cold box 2 comprising:         -   at least one heat exchanger;         -   a fixed assembly zone 8 on its outer wall;     -   a device 3 for the various equipment required for implementing         the cold fluid required for the liquefaction of a natural gas         stream from a hydrocarbon supply stream;     -   an interconnection module 4 comprising a pipe holder means and a         set of pipes, control valves, and electricity connection and         instrumentation 5, 6, 7, designed to connect said at least one         cold box 2 to the at least one equipment device 3 for the cycle         for refrigerating and/or separating C6+ type hydrocarbon         elements contained in the natural gas.

The interconnection module 4 rests on a frame that allows it to be handled and is connected to the cold box in the vicinity of said assembly zone.

Advantageously, the interconnection module comprises one or more elements selected from among control valves, manual valves, valve actuators. Thus, the important elements for controlling the liquefaction assembly are arranged in the interconnection module, the assembly and the on-site handling of which are simpler and safer, which facilitates the assembly of these elements and facilitates access for maintenance. The safety of the unit is improved. In particular, one or more valves are of the Pressure Safety Valve (PSV) type. According to a particular embodiment, the unit comprises one or more pressure safety valves, all of which are arranged in the interconnection module.

The feed stream NG can be a stream of natural gas, which can be pre-treated, in which one or several substances, such as sulphur, carbon dioxide, water, are reduced, so as to be compatible with cryogenic temperatures, as is known in the prior art.

The heat exchangers are known from the prior art and can have various arrangements of their feed flows and refrigerant streams.

When the flow of liquefied, or at least partially liquefied, hydrocarbons is liquefied natural gas (LNG), the temperature can be approximately −150° C. to −160° C.

The liquefaction of the feed stream NG is carried out by virtue of a fluid or an expanded cooling nitrogen current in one or more coolant circuits for pre-cooling the feed stream NG.

A heat exchange module comprises walls for thermally insulating the heat exchanger from the outside and comprises a framework allowing the heat exchange module to be transported so that it can be fixed.

The framework can be made of stainless steel bars in order to reduce the effects of thermal diffusion. Furthermore, this framework can assume the form of a container, thus forming the edges of a rectangular parallelepiped, also referred to as a right cuboid. Thus, it is simple to transport. The framework of the heat exchange module can also comprise means for facilitating installation.

An element is understood to be a module, or a compressor, or an expansion device or a circuit of a module, or a cooler, or a separator.

Connections are understood to be a tube or pipe that may or may not be insulated and that can comprise valves or restrictors.

A stream is understood to be one or more fluids, that may be in the liquid phase or in the gaseous phase or both, circulating through elements of the system.

An inlet is understood to be a point at which the fluid enters, therefore giving the stream a direction of circulation. In other words, an inlet of a first element is connected downstream of an outlet of a second element.

An outlet is understood to mean that the fluid exits an element and therefore provides a direction of circulation for the stream. In other words, an outlet of a first element is connected upstream of an inlet of a second element.

Connected means connected for transporting a fluid, for example, an inlet connected to an element implies that a fluid can transition from the element to the inlet either directly or via other elements.

Connected is understood to mean the connection of two elements (the outlet of one element to an inlet of another element) for transporting fluid using connections or connected directly to one another (an outlet directly connected to an inlet of an element (without pipe)). In other words, there are no other elements between the two elements.

Fixed is understood to mean the physical assembly of one element to another element in order to secure them together.

An expanded stream is understood to mean the stream downstream of an expansion circuit and upstream of a compressor.

A compressed stream is understood to mean the stream upstream of an expansion circuit and downstream of a compressor.

The liquefied natural gas resulting from the method that is the subject matter of the present invention subsequently can be, for example, transferred to a storage or transportation device.

The method that is the subject matter of the present invention particularly enables the investment expenditure to be optimized. Indeed, having a modular system allows several arrangements of the modules to be proposed and thus allows the installation research costs, as well as the manufacturing cost, to be reduced.

It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus; the present invention is not intended to be limited to the specific embodiments in the examples given above. 

1. Natural gas liquefaction unit comprising: at least one cryogenic cold box (2) comprising: at least one heat exchanger; a fixed assembly zone (8) on its outer wall; at least one closed loop nitrogen refrigeration cycle; at least one device (3) for equipment required for implementing the liquefaction of a natural gas stream from a hydrocarbon supply stream; at least one interconnection module (4) comprising a pipe holder means and a set of pipes and valves (5, 6, 7), designed to connect said at least one cold box (2) to at least one equipment device for the cycle for refrigerating and/or separating C6+ type hydrocarbon elements contained in the natural gas, characterized in that the interconnection module (4) rests on a frame allowing it to be handled and is connected to the cold box (2) and to the other method or equipment sub-assemblies (3) located around said fixed assembly zone (8).
 2. Unit according to the preceding claim, characterized in that the interconnection module (4) particularly comprises one or more elements selected from among control valves, manual valves, sample connections, pipes, pre-cut panels with valve actuators, instruments, vapour sources, lighting, ladders and platforms, pre-wired junction boxes, platforms for instrument/electric cables, pipe supports, channeling.
 3. Unit according to claim 2, characterized in that the interconnection module (4) comprises one or more elements selected from among control valves, manual valves, valve actuators.
 4. Unit according to one of the preceding claims, characterized in that said other method or equipment sub-assemblies (3) are required to implement at least one method function selected from among the compression of the nitrogen of the refrigeration cycle, the overpressurization of the nitrogen of the refrigeration cycle, the expansion of the nitrogen of the refrigeration cycle, the cooling of the nitrogen of the refrigeration cycle, the liquefaction of the natural gas stream, the separation of the C6+ type hydrocarbons contained in the natural gas, the interconnection module (4) being devoid of such method or equipment sub-assemblies.
 5. Unit according to one of the preceding claims, characterized in that the refrigeration cycle comprises a first means for compressing the nitrogen of the refrigeration cycle, a means for cooling the nitrogen of the refrigeration cycle, a second means for compressing the nitrogen of the refrigeration cycle, said second compression means comprising two booster compressors coupled to two respective expansion means, said booster compressors being configured to compress the nitrogen of the refrigeration cycle at an identical pressure.
 6. Unit according to one of the preceding claims, characterized in that said frame has a metal structure.
 7. Unit according to one of the preceding claims, characterized in that said at least one heat exchanger is a brazed aluminium heat exchanger.
 8. Use of a unit as defined in one of the preceding claims for liquefying a natural gas stream.
 9. Method for starting a liquefaction unit as defined in claims 1 to 6, comprising the following steps: on-site installation of a closed loop nitrogen refrigeration cycle and of a cold box (2) comprising: at least one heat exchanger; a fixed assembly zone (8) on its outer wall; on-site installation of an interconnection module (4) comprising a pipe holder means and a set of pipes and valves (5, 6, 7), designed to connect said at least one cold box (2) to at least one equipment device (3) for the cycle for refrigerating and/or separating C6+ type hydrocarbon elements contained in the natural gas; fixing said interconnection module (4) to the cold box (2) and to at least one equipment device (3), allowing the implementation of the liquefaction method using said cold box (2), already available on the site. 